In recent years, a liquid crystal display device, particularly a color liquid crystal display device including a TN mode liquid crystal display panel (TN mode liquid crystal panel, TN panel), has come to be commonly used in a field where a CRT (Cathode Ray Tube) has been used.
For example, document 1 (listed hereafter) discloses a liquid crystal display device that switches driving methods of a TN panel in accordance with whether an image to be displayed is a video image or a still image.
Incidentally, such a TN panel has a problem in its viewing angle property, as compared with a CRT.
As a viewing angle (angle with respect to the panel; an angle with respect to a normal direction of the panel) becomes wider, a gradation property varies. Accordingly, there occurs gradation reverse at some angles.
In light of this, what have been conventionally developed are (i) a technique for improving the viewing angle property by using an optical film and (ii) a technique for restraining the gradation reverse by devising display methods.
For example, disclosed in each of documents 2 and 3 (listed hereafter) is a method for improving the viewing angle by dividing a single frame so that a plurality of signal writings are carried out with respect to one pixel, and by combining the voltage levels of the signal writings.
Further, a liquid crystal display panel such as a TV (television receiver) requires a wide viewing angle. Therefore, for acquirement of the wide viewing angle, such a liquid crystal display panel adopts a liquid crystal of the IPS (In-Plane-Switching) mode, the VA (Vertical Alignment) mode, or the like, instead of the TN mode.
For example, a liquid crystal panel (VA panel) adopting the VA mode realizes a contrast of 10 or greater at an angle of 170° or less vertically and horizontally with respect to the VA panel, and prevents the gradation reverse.
Document 1: Japanese Laid-Open Patent Publication Tokukai 2002-23707 (published on Jan. 25, 2002);
Document 2: Japanese Laid-Open Patent Publication Tokukaihei 05-68221/1993 (published on Mar. 19, 1993);
Document 3: Japanese Laid-Open Patent Publication Tokukai 2001-296841 (published on Oct. 26, 2001);
Document 4: Japanese Laid-Open Patent Publication Tokukai 2004-78157 (published on Mar. 11, 2004);
Document 5: Japanese Laid-Open Patent Publication Tokukai 2003-295160 (published on Oct. 15, 2003);
Document 6: Japanese Laid-Open Patent Publication Tokukai 2004-62146 (published on Feb. 26, 2004);
Document 7: Japanese Laid-Open Patent Publication Tokukai 2004-258139 (published on Sep. 16, 2004); and
Document 8: Color Science Handbook, second edition, (University of Tokyo Press; published on Jun. 10, 1998).
However, even the VA panel which is thought to realize a wide viewing angle, cannot completely eliminate variation in the gradation property, due to variation in the viewing angle. For example, the wider the viewing angle is in a horizontal direction, the more the gradation property is deteriorated.
That is, as illustrated in FIG. 2, when changing the viewing angle from 0° (front of the panel) to 60°, a gradation γ property accordingly varies, thereby causing such an excess brightness phenomenon that a luminance in halftone becomes excessively high.
Also in a liquid crystal display panel adopting the IPS mode, its gradation property varies to some extent as the viewing angle is wider though the variation of the gradation property depends on how an optical characteristic of an optical film is designed.